Over a period of use, the casing or liner within the well bore of an oil or natural gas well becomes covered with hard deposits. These deposits must be periodically removed or they can build up to levels of thickness and hardness where they can adversely effect efficient operation of the oil well.
Cleaning involves spraying or jetting the inner wall of the casing with cleaning fluid at very high pressure to break up and dislodge the deposited material. This is achieved by means of a cleaning device with jetting nozzles in the sides of it which is lowered down into the well bore casing on the end of a drill string. Once a section of the well bore casing has been jet cleaned, the cleaning device is withdrawn from the well bore casing and removed from the end of the drill string. The drill string is then returned to the well bore casing where cleaning fluid is run down through it to a point below the section of the well bore casing which has been jet cleaned. The cleaning fluid rises up inside the space between the well bore casing and the drill string and as it does so, it carries material broken up and dislodged during the jetting operation to the top of the well bore casing. In this way the well bore casing is flushed clean. This operation is repeated as many times as is necessary to clean the well bore casing of deposited material from top to bottom.
While the method of cleaning described above is effective, it is also very time consuming in that the cleaning device must be repeatedly inserted into the well bore casing to allow for jet cleaning and then withdrawn to allow the material cleaned away from the wall of the well bore casing to be flushed out. During a cleaning operation the well is, of course, not producing oil or natural gas. This downtime is costly and therefore undesirable.
The problems arising from material building up within a well bore are not, of course, restricted to the riser liner of the well bore. Material may also build up below this which it is preferable to dislodge and remove from the well bore.